1. Field of the Invention
This invention relates to a conveyor mechanism for a thin plate, and more specifically to an apparatus adapted to convey thin plates one after another from one treatment or processing table to another, for example, upon heating and drying thin plates such as semiconductor substrates (hereinafter called "wafers") or glass plates, which have in advance been coated with a photoresist automatically on a heating table and then cooling same on a cooling table.
2. Description of the Prior Art
Reference is first of all made to FIGS. 1 and 2 illustrating a conventional conveyor mechanism which has generally been used, in which there are shown a wafer 1 bearing a photoresist coated on the upper surface thereof, belt conveyors 2,2, a heating table 3, vertical grooves 4,4 formed in the upper surface of the heating table 3 at locations underneath the belt conveyors 2,2, an annular groove 5 formed in the upper surface of the heating table 3 and having a diameter substantially equal to the diameter of the wafer 1, and positioning pins 6,6.
In the illustrated mechanism, the wafer 1 which has been conveyed by the belt conveyors 2,2 and has been stopped above the annular groove 5 by means of the positioning pins 6,6 is mounted on the heating table 3 by either lowering the belt conveyors 2,2 relative to the heating table 3 or raising the heating table 3 relative to the belt conveyors 2,2 so that the belt conveyors 2,2 are received in their corresponding longitudinal grooves 4,4. Thereafter, the thus-mounted wafer 1 is sucked in place on the heating table 3 by means of a vacuum suction holder (not illustrated) and is then heated and dried.
In such a conveyor mechanism, the photoresist is softened in the course of the heating and drying of the wafer 1 on the heating table 3 because the photoresist becomes hotter. In some instances, the photoresist runs down from the circumference of the wafer 1 onto the annular groove 5 of the heating table 3 and the belt conveyors 2,2. When conveying the wafer 1, the photoresist adhered to the belt conveyors 2,2 may smear the rear surface of the wafer 1.
Furthermore, the wafer 2 is not heated at parts, which lie over the longitudinal grooves 4,4 of the heating table 3, by the heating table 3 directly. Thus, the temperature distribution becomes uneven in the wafer 1, leading to non-uniform drying of the photoresist.
The uniform drying of each photoresist has become an important issue, because integrated circuit (IC's) have been densified more and more and larger wafers have been more popularly employed in recent years.
In the meantime, there was proposed such a conveyor mechanism as depicted by way of example in FIGS. 3 and 4.
In FIGS. 3 and 4, numerals 11, 12, 13 and 14 correspond respectively to numerals 1, 3, 4 and 5 in the above-described prior art conveyor mechanism and thus indicate a wafer, heating table, longitudinal grooves and annular groove respectively.
Numeral 15 indicates a conveyor frame, which is constructed by connecting rectangular frames 16,16, which extend longitudinally from the rear to the front of the conveyor mechanism and are parallel to each other, together at their bottom frames by means of connecting bars 17. A plurality of upward projections 18 is provided on the upper edges of the top frames 15a,15a at desired locations.
The conveyor frame 15 moves by drive means (omitted in the drawings) as illustrated by imaginary lines in FIG. 3. Thus, the conveyor frame 15 supports the wafer 11 bearing a photoresist coated thereon, which has been fed by belt conveyors 19, upwardly by the projections 18 and then conveys it to a position right above the heating table 12.
Then, the conveyor frame 15 moves downwardly. This causes each of the top frames 15a,15a and each of the projections 18 to sink fully within their corresponding longitudinal grooves 13,13. At the same time, the wafer 11 is sucked on the heating table 12 and is then heated and dried there.
The above-proposed conveyor mechanism may avoid smearing of the rear surface of each wafer 11 by a photoresist if the projections 18 are arranged to support the wafer 11 at locations somewhat inward from the circumference of the lower surface of the wafer 11. However, the conveyor mechanism is still unable to avoid non-uniform drying since there are the longitudinal grooves 13,13.
Although no drawings are incorporated herein, air film conveyors are also employed to convey wafers. They are however accompanied by such drawbacks that a wafer is shaken during its conveyance and is thus brought into contact at a circumferential part of its lower surface with the surface of a heating table, thereby causing its photoresist to stick on the surface of the heating table; and blown-up dust deposits on the surfaces of the wafer.